The present invention relates generally to relates to components manufactured with steps including compression and clamping. More particularly, the present invention relates to precise control of such compression and clamping.
Systems such as disc drives and ring laser gyroscopes require stacked mechanical components having shapes defined with a very high precision. Some of these components are very thin, and can be warped or cracked by the application of high clamping forces. High clamping forces are frequently necessary, however, for stable retention of components.
Disc clamps for magnetic hard disc drive spindles have as their primary objective the clamping of the magnetic hard discs in a stack onto the spindle so that the discs do not shift radially under shock. To minimize mechanical distortion, which is made worse with large temperature shifts, it is desirable to use friction contact rather than to rely upon adhesives or screws to prevent radial shift. Such a shift, otherwise known as xe2x80x9cdisc slipxe2x80x9d, typically results in total failure of the disc drive due to misalignment of the pre-recorded tracks on the slipped disc from the pre-recorded tracks on the other discs.
One or more discs are held in position by adjacent layers. Spacer layers are positioned between discs. The required disc clamping force is conventionally determined by the shock specification of the disc drive. For example if the disc drive specification requires that the disc drive withstand a shock of 300 G""s, a radial friction force F of about three pounds must be applied to resist disc slippage. With conventional materials, the clamp/disc interface has a coefficient of friction (xcexcs) of 0.15. The axial (normal) force magnitude N necessary to provide this friction is thus F/xcexcs =3 lbs./0.15=20 lbs.
As disc drives become smaller, they are also becoming thinner. This puts severe constraints on the overall stack height of the disc/spindle assembly, which in turn, necessitates a reduction in the thickness of the discs and the height of the disc clamp above the spindle. As discs become smaller, there is also a tendency for the discs to warp into a saddle shape due to the required clamping force of the disc clap to prevent xe2x80x9cdisc slipxe2x80x9d. For these reasons, new disc clamping approaches are required.
One approach suggested in PCT Application No. WO93/06599 is to employ an annular clamp and spacer having a plurality of fingers exerting a radial pressure on a first disc and a plurality of projections bearing on a second disc to control radial movement of the first disc and the separation of the two discs.
Another approach is suggested in IBM Technical Disclosure Bulletin Vol. 32, No. 6, November 1989, page 129, Disc Pack Assembly Design, which describes the use of a grooved spliting to clamp a plurality of discs. Each disc rests in a groove in the ring which is squeezed and slipped into the internal diameter of the discs, when the ring is released it exerts a radial clamping force on the discs.
None of the existing approaches provides a manufacturing process for precise control of clamping force that ensures adequate clamping without unduly stressing delicate layers. All of them, moreover, require changes to at least one component of every stack, which can incur added costs and/or performance losses.
The present invention is an improved method of controlling the compression of multi-layer stacks without the need for modifying components in every stack. It includes steps of assembling a first stack with a force sensor between two of its layers, and compressing the stack with an initial force value. An improved force value is derived, at least in part, from a signal received from the force sensor. A second stack is assembled and compressed using the improved force value. Numerous xe2x80x9csecond stacksxe2x80x9d can be made in this manner without substituted components.
The present invention optionally includes steps of clamping the first stack, waiting 0.1 to 10 seconds, releasing the platform-exerted force, and then extracting a measured force value from the received signal. It optionally includes steps for making additional stacks with or without sensors or otherwise to generate several signals to acquire useful measurements. For instance, optional steps are provided for determining the fate of one stack (i.e., preserving or discarding) by the performance of another. Additionally, specific embodiments are presented of components and systems that are improved from those of the prior art by use of the inventive method.